Tests of Rock Cores, Pembine Study Area, Michigan and Wisconsin.

Laboratory tests were conducted on rock core samples received from six core holes in the Pembine Area of Dickinson County, Michigan, and Marinette and Oconto Counties, Wisconsin. Results were used to evaluate the quality and uniformity of the rock to depths of 200 feet below ground surface. The core was identified as predominantly tonalite, granite, amphibolite gneiss, and biotite gneiss, with relatively insignificant quantities of quartz gneiss and biotite schist. Evaluation of the Pembine Area core on a hole-to-hole basis indicates that the granite removed from Hole PB-CR-20 and the biotite and quartz gneiss removed from Hole PB-CR-40 are quite competent materials and should offer good possibilities as competent hard rock media. The tonalite and amphibolite gneiss removed from Hole PB-CR-27 were found to be relatively competent rock, with only one specimen, an amphibolite gneiss, yielding physical test results characteristic of marginal quality rock. Generally, this yielded material that should offer some possibility as a competent hard rock medium. Holes PB-CR-2, -10, and -16A generally yielded rock core that exhibited rather varied physical properties. Though much of the rock was relatively competent in quality, several specimens that were removed from depths greater than 50 feet below ground surface in each hole were found to be quite incompetent.